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Gabriele Stoll
Natural Crop Protection in the Tropics
Letting Information Come to Life
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Methods of Field Protection
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Insects
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Promoting natural enemies
One of the most important components of
integrated pest management is the management of natural
enemies. These include the parasitoids, arthropod predators and
pathogens, but also the larger predators such as frogs, toads,
birds, lizards, and snakes. Promoting natural enemies is not
only for the specialist entomologists and companies which sell
pathogens and beneficial insects, but is the prime task of the
farmer. Promoting natural enemies means managing the farm to
create a friendly environment for these pest management 'farm workers'.
Awareness of their benefits and needs enables farmers to create
the optimal environment so that they can do a good job. The
optimal environment means firstly a diversified farming system
that creates suitable habitats for the natural enemies, so that
they are on site when needed. Intercropping and mixed cropping
as described in the "Intercropping" section above
contribute to this. Secondly it means managing these
assistants, delegating the work to them by giving them signals
showing where exactly their action is required. Thirdly it
means farmers actively protecting, promoting and propagating
them. Some of the signals and methods that are based on
practical experience are presented below.
Ants have been found to be good
predators of a number of insect pests, particularly the
carnivorous species such as weaver ants, soldier ants, and
others. As they are social insects and do not move widely they
are reasonably easy to manage. Ants are the most important
group of predators in Africa, comparable to the spiders in
Southeast Asia. The following sections give some practical
ideas for managing and promoting ants.
Attracting ants with sugar-water
This technique is based on the idea of
applying 'artificial honeydews' to crops to concentrate natural
enemies in the field. Such honeydews can be made from sugar,
jaggery, molasses etc., and consist of sucrose and/or proteins,
which are nutrients to natural enemies. Applying them to crops
has been shown to attract ants, but also ladybird beetles,
lacewings, hover flies, big-eyed bugs, and minute pirate bugs.
This technique could be a very attractive alternative to
pesticides for small farmers in the tropics, thanks to low/no
risk of poisoning in application, the ease of preparation and
application, and the ready availability of sucrose sources.
An example is the application of sugar
solution for the control of the fall
armyworm, Spodoptera frugiperda.
This was developed as a joint effort between farmers and
scientists. In a training course on natural pest control in
Honduras, farmers learned about the benefits of natural enemies
and their biology. In this course, Sra. Maria Castro learned
that ants were predators of insect pests. Having previously
observed that ants like sweet things, she began using a
sugar-water solution to attract ants to her maize field for
control of fall armyworm. Subsequently, an experiment was set
up to observe the activity of natural enemies in maize treated
with sugar solutions. A sugar solution was prepared using 90 g
sugar per litre water. For one hectare, about 17 kg of sugar
are needed. The applications began one week after plant
emergence, and were conducted at weekly intervals for five
weeks until the maize reached a height of 1.5m.
The following observations and
recommendations resulted from this study:
On average, twice the numbers of
predators were found in maize treated with sugar than in the
non-treated maize.
The most abundant predator recorded
was the fire ant, Solenopsis
geminata. Other predators were
ladybird beetles, spiders, lacewings, assassin bugs, and social
wasps.
Leaf area damage was 35% less in
sugar-treated maize than in non-treated maize, whereas whorl
infestation was 18% less in maize treated with sugar. This lead
to the conclusion that fire ants predate the smaller larvae
more than the larger larvae that cause the whorl damage.
The printed version contains more
information about:
Weaver ants in orchards and groves
Soldier ants
Beetle larvae control
Attracting birds with turmeric-rice
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